THE BASIN PROVINCE 117 



According to Darton, such rocks occur in the Zuni UpHft, at Ojo Caliente, 

 and in the Nacimiento Mountains, all in northwestern New Mexico. 



More directly north of the Guadalupe Mountains, but still west of the 

 barrier between the two provinces, limestone of this horizon occurs in con- 

 siderable quantity. Lindgren says that a considerable thickness of Penn- 

 sylvanian limestone existed over the whole State, with a maximum thickness 

 between Santa Fe and Las Vegas. As far south as Socorro there is an 

 alternation of shale and sandstone with the limestone, but south of this 

 point limestone predominates, with a decrease in the total thickness. All 

 the conditions indicate shore conditions in the northern part of the State, 

 where some land existed even at this (Pennsylvanian) time. The land 

 mentioned by Lindgren was, in part at least, the barrier between the Plains 

 and Basin Provinces. 



(b) Conditions in New Mexico. — The upper Paleozoic rocks of New Mexico 

 are divided into the Manzano formation and the Magdalena formation. The 

 latter, and lower, is entirely Pennsylvanian, the former is in part Permo- 

 Carboniferous. 



Near Socorro, the Magdalena formation is nearly 1,500 feet thick, divided 

 between the upper Madera blue limestone and shale and the lower Sandia 

 limestone and shale, with minor quantities of sandstone. Lee^ gives a 

 description of this limestone in its relation to the Manzano formation in 

 central New Mexico. He says that in late Magdalena time an uplift, or 

 other change, occurred in the mountain region of New Mexico which caused 

 a change of sediment from limestone to red beds. In the Mimbres Moun- 

 tains, near Kingston — 



"The basal Magdalena strata consists of about 300 feet of dark-blue and gray 

 limestone in thick beds with thin shale partings. The upper part of the group 

 has about the same thickness and consists chiefly of blue and drab shales inter- 

 stratified with several beds of limestone 15 to 20 feet thick. Unconformably 

 overlying these beds are red sandstones and shales (Abo sandstone) of the Man- 

 zano group. * * * There is no evidence on which to separate the group into 

 Sandia formation and Madera limestone, as in the region farther west." ' 



(c) Conditions in Arizona . — In southern Arizona the Pennsylvanian (?) 

 limestone appears at Bisbee and Globe. Describing the first area, Ransome* 

 says: 



"The Naco limestone * * * is made up chiefly of light-colored beds, which 

 consist essentially of calcium carbonate. The beds range in thickness from a 



^ Lindgren, VV., L. C. Graton, and C. H. Gordon, Ore Deposits of New Mexico, U. S. Geo- 

 logical Survey, Professional Paper No. 68, pp. 31-32, 1910. 



' Lee, W. T., and G. H. Girty, The Manzano group of the Rio Grande Valley, New Mexico, 

 U. S. Geological Survey Bull. 389, 1909. 



' Darton, W. H., A Comparison of the Paleozoic Sections in Southern New Mexico, U. S. 

 Geological Survey, Professional Paper 108-C, p. 53, 1917. 



* Ransome, F. L., The Geology and Ore Deposits of the Bisbee Quadrangle, Arizona, U. S. 

 Geological Survey, Professional Paper No. 21, p. 45, 1904. 



